A study of the performances of low-temperature heating systems

significance Statement

Because of the reduction of the world fossil fuel reserves and strict environmental protection standards, one main research direction in the construction field has become the reduction of energy consumption, including materials, technology, and building plans with lower specific energy need, on one hand, and equipment with high performance on the other hand.

The operation of central heating systems at reduced supply temperature results in considerable energy savings. After a thermal rehabilitation of the building, the exceeded surface of existing heaters and the decreased heat load of system can be adjusted to the new conditions by reducing the supply temperature.

This study showed that radiant heating panels works better than radiator heating. In well-insulated buildings, the energy consumption of the radiator heating system is up to 10% greater than that of the floor heating system, which also provided good thermal comfort. In well-insulated buildings, a floor heating system is recommended over a radiator heating system if a heat pump is used as the energy source. However, in this case, a radiator heating system can be designed for low water temperatures because of the smaller differences in the COPsyst (system coefficient of performance) value. There is no reason to use higher than 55/45 °C design water temperatures in well-insulated buildings.

The proposed analytical model of thermal emission for radiant floors was validated by the measured values, and a reasonable agreement prevailed. This model permits the determination of the floor surface temperature at any point on its surface and the emitted mean heat flux.

The floor-ceiling heating system has the best performance in terms of the lowest energy consumption, operation cost, CO2 emission, and the nominal boiler power. In addition, it is important to note that the next best performing radiant system is the system with the wall heating panel. The classical ceiling heating system displays the worst performances in terms of the listed parameters.

The comparison of the room operative air temperatures and the set-point operative air temperature indicates that all radiant panel systems provide satisfactory results without significant deviations.

New investigations should be performed to examine other low-temperature heating systems and their combinations.

In Europe, high energy consumption in the building environment has raised the need for developing low-temperature heating systems both in new buildings and in retrofitting buildings. This paper addressed many different topics related to energy saving in central heating systems with reduced supply temperature and radiant panel heating including floor heating, ceiling heating and wall heating. The paper investigated the performance of these different types of low-temperature heating system using numerical modelling, simulation tools and also site measurements. Thus, energy performance of radiator and radiant floor heating systems connected to a ground-coupled heat pump (GCHP) is compared, as obtained with experimental measurements in an office room. Furthermore, the thermal comfort of these systems is compared and a mathematical model for numerical modelling of thermal emission from radiant floors is developed and experimentally validated. Additionally, a comparative analysis of the energy, environmental and economic performances of floor, wall, ceiling and floor-ceiling heating using numerical simulation is performed. Finally, the energy efficiency of a heat pump in conjunction with a radiator or radiant floor heating system is calculated for different supply, return, and air design temperatures. This study showed that floor-ceiling heating works better than other low-temperature heating systems regarding providing better thermal comfort, lower energy consumption, lower CO2 emission and lower operating cost.

About the author

Ioan Sarbu is a professor and head of the Department of Building Services Engineering at the Polytechnic University of Timisoara, Romania. He obtained a diploma in Civil engineering from the “Traian Vuia” Polytechnic Institute of Timisoara in 1975 and a Ph.D. degree in Civil engineering from the Timisoara Technical University in 1993. He is a European Engineer designated by European Federation of National Engineering Associations (Brussels) in 2001.

His main research interests are related to refrigeration systems, heat pumps and solar energy conversion. He is also active in the field of thermal comfort and environmental quality, energy-efficiency and energy savings, and numerical simulations and optimisations in building services. He involved in preparation of regulations and standards related to energy and environment, and is a specialist for renewable and energy certification. Additionally, he is a member of the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), International Association for Hydro-Environment Engineering and Research (IAHR), Romanian Association of Building Services Engineering (RABSE), and Society for Computer Aided Engineering (SCAE). He is doctoral degree advisor in the civil engineering branch, an expert reviewer on the National Board of Scientific Research for Higher Education (Bucharest), vice president of the National Board of Certified Energetically Auditors Buildings (Bucharest), a member of the National Council for Validation of University Titles, Diplomas and Certificates, a member of the Technical Council for Civil Engineering from Ministry of Regional Development and Public Administration, and a reviewer of the Journal of Thermal Science and Technology, Energy Conversion and Management, Applied Thermal Engineering, International Journal of Refrigeration, International Journal of Sustainable Energy, Energy and Buildings, and Energy Efficiency.

He has published 12 books, 6 book chapters, more than 120 articles in indexed journals and about 50 articles in proceedings of international conferences. He is also author of 5 patent certificates and of up to 20 computer programmes, supervisor-mentor of 15 PhD students, more 40 Master student and more than 200 engineering students.

About the author

Calin Sebarchievici is a lecturer in the Building Services Engineering Department at the Polytechnic University of Timisoara, Romania. He obtained a diploma in building services engineering from the Polytechnic University of Timisoara in 2003. He received his master’s degrees from the same university and Bolognia University, Italy in 2004 and 2007, respectively, and his PhD degree in civil engineering from the Polytechnic University of Timisoara in 2013.

His research is focused on air-conditioning, heat pump and refrigeration systems. He is also active in the field of thermal comfort, energy efficiency, and energy savings. Additionally, he is a member of the ASHRAE, RABSE, and GEOEXCHANGE Romanian Society. He is co-author of 1 book, 2 book chapter, 15 journal articles and more than 10 conference proceeding publications.